iNaturalist sightings are fed into gbif.org and obis.org, the two major databases of biological sightings that collate everything.
From my experience in my niche, iNaturalist sightings generally agree with the 'professional' sightings in the same database (various scientific expeditions' sightings data). It's definitely valuable data!
Of course, it has some interesting biases, for starters, small species and fast species are generally not submitted because it's hard to take good photos. But scientific expeditions also have their own biases; if they use underwater nets, for example, they'll also select for larger animals.
Of course, it has some interesting biases, for starters, small species and fast species are generally not submitted because it's hard to take good photos. But scientific expeditions also have their own biases; if they use underwater nets, for example, they'll also select for larger animals.
Some data is far better than no data!